[Ronie1988]

For use in educational and hobby purpose those may not need certificate….but for commercial and industrial use , yes, they need certificate as per standards

[Ronie1988]

Dear sir,

The RFID module available on market which is RC522 (MFRC522) module is based on SPI port. One pin on SPI port is slave select or SS which is used to select a particular module by a pin and use that to read cards. Please refer to widely used Github library for arduino https://github.com/miguelbalboa/rfid .

However RC522 is not fully working with NFC. NFCs are just a step ahead of RFID in technology. However there are PN532 modules in market and you can use those with Arduino. Goodluck

[Ronie1988]

There are plenty of RC kit like FlySky, Radiolink etc that can jumpstart your project. However you may also search for RC kits compatible with the radio receiver inside the tugboat model you are having.

[Ronie1988]

LM1117 is linear regulator with low drop. However the factors are input voltage and high current. The regulated voltage is output and the the difference of input and regulated voltage is dissipated in form of heat when multiplied with current. Please use heat sink or lower input voltage as per datasheet.

[Ronie1988]

The load might be oscillating. The issue maybe a mechanical thing. However as you have said that you already are using a shielded cable, try to use shielded twisted pair like CAT-6 cable. Also in the input section of the HX711 module try adding filter capacitor. Make sure power supply is clean and setup is away from a EM noise source.
Also as you said that you have used a mux (perhaps analog), have you compensated for voltage drop in mux by adding voltage buffer at the end of Mux output ? Please share diagram to enable us to help you further

[Author]

Posts